Filter casing and process of operating the same



Aug. 26,v 19.30.

E. J. swEi-:TLAND 1,774,044

FILTER CAS-ING AND PROCESS OF' OPERATING THE SAME Filed oct. 28, 41925 6 sheets-Sheet 1 Traa/mrs.

AU8- V26, l930- E. J. swEETLAND l 1,774,044

VFIL'LERVCASING AND'PRocEss oF OPERATIG THE SAME Aug. 26, 1930.

I E. J. swr-:ETLAND FILTR CASING AND PIROCESS/ 0F OPERATING THE SAME Filed oct. 2 8, 1925 e sheets-sheet 3 'ERNEST J7 ..\/v I SHHHHH|||I|||`- T NWNMUUNHMUW a, 3. vmw. No Il. Il i .nu HMHHH Aug. 26, 19,30.

E. .LSWEETLAND 1,774,044 vFILTER CASING AND PRCESS OF OPERATING, THE SAME V Filed oct. 28, 1925A 6 Sheets-Sheet 4 TLAN D Aug. 26,1930. E. J. swEErLAND l FILTER cAsING'AND PRocEss OF'QPERATING 'rma SAME Filed oct'. 28, 1925 e sheets-snakty 5.

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ATTO/:wins

ug.`26,1930.' v E .J. swEETLANb 'A 1,774,044

,FILTER CASNG ANDP'ROCESS OF OPERATING THE SAME Fild opt. 28. 1925 e sheets-sheet s Fig; 9-

/M/ENTOR ATTO/wins;

Patented Aug. 2s, 1930 UNITED sTATEs ERNEST .'r. swnE'rLANn, or HAzLEToN, rnNNsYLvAnn IEIIJJIIIIB.v CASIN'G AND PROCESS OF DIPERATNG THE SAME Application medomber as, 1925. serial No. 65,292.

The present invention relates to a-method and apparatus or'use in conjunction with that class `of filters commonly lmown as the vacuum filters, or suction filters, and is par- 5l ticularly applicable to the continuous types of filters known in the trade as the American continuous filter; and the drum type of filter, .of which type the so called Oliver filter vis representative.l Y

It should' be clearly understood that my invention' relates entirely to the casing or housing and to the method of operating same and I do not claim the invention of the details of the filters herein shown and described l5 for the purpose of illustrating typical uses of my invention; nor do I wish to be limited in the use of myinvention tothe speciic types of lters herein described, forthe filter casing orvr housing may be employed in conjunction with any type of filter wherein its use may be found advantageous.

I am aware of the fact that eiiorts have been made to build continuous rotating drum filters and continuous rotating disc filters in 'such a manner that the lter is operated under a pressure greater than atmospheric pressure. These efforts, however, have been along entirely different lines from the present invention and have involved a highly special design of filter, the very nature of which has made them very expensive in construction and in many particulars objectionable from a standpoint of accessibility and convenience in ,making adjustments, repairs and replacements.

An outstanding advantage of the method and apparatus described herein resides in the fact that the invention may be applied to any standard type of vacuum orsuction iilter now in use without making any important changes or modifications, and by the use of the invention the capacity of such lilters may be increased from 200 to 500 per cent.

A further advantage of the invention is that` the purchaser of a drum or disc type of suction filterv may -use his lter alternately as a suction or pressure filter at his pleasure`without any changes in the filter construction.

The advantages from the standpoint of first cost are at once obvious. j In many cases one filter unit operated under a pressure of say 50 pounds per square inch may do the work of four units of similar size operated by suction. Assuming each unit to cost $10,000.00 the required filters operated by suction would cost $40,000.00 whereas when the present invention .is employed a single unit costing $10,000.00 plus a suitable casing at a cost of say $3,000.00 will do the work, with a resultant saving of $27,000.00 in installationcost, in additionto the saving in floor space, cost ofsupervision, etc.

A further advantage' lies in the fact that cost ofsupervision, maintenance, repairs, de-

preciation, etc. are naturally much less with one unit than with a plurality of units of the same size. l

A still further `advantage is that many materials which are not at present amenable to liltration in suction type filters could successfully be used `with the same type of filter when employed in conjunction with the casing herein described. For example at the present stage of the art the first carbonation juices in beet sugar factories cannot successfully be filtered with any type of suction filter because the capacity of such lters on beet sugar juices is so. low that an installation of continuous suction filters becomes inordinately expensive. Furthermore the cake formed with this material on continuous suction filters is so thin thatit is diicult to discharge from the filter cloth.

The result is that in present practice no attempts are made to handle the juices in continuous' suction filters until the juice has first been put through a preliminary filtering or thickening process. But by the use of the pressure casing herein described the first carbonation juices may be filtered directly upon the present types of suction filters without any preliminary treatment and with a -v ery reasonable cost f installation and operatlon.

A further advantage of my invention resides in the fact that the purchaser of a lter casing of the type described is not confined to the use of any particular type of suction filter., The casing when once purchased is a permanent a'sset'and may be used 100 in conjunction with any type of suction filter, and the filter may be replaced by a new one either of the same type, or by a filter of different type after the first one has been worn out, or for any other reason discarded. Another advantage is that the filter may if desired be conveniently removed from this casing for repairs or replacements, and in the event that extensive repairs or ageneral overhauling becomes necessary a substitute filter may be operated in its place during the interim and production thus maintained.

Another advantage of my invention is that a suitable lock is provided whereby a workman may enter the casing to make minor repairs or adjustments, or to study the operation of the filter, without reducing the pressure Withinl the ychamber and without interruption to the operation of the filter. vReferring to the drawings, Fig. 1 shows a transverse section of the casing taken approximately at 2-2 of Fig. 2 and represents an American type of filter in place within the casing, with a man represented along side the filter to give an idea of proportions. The fiexible conduitsby means of which the filter is connected to the outside pipe lines during operation are here represented as being disconnected.

Fig. 2 is a si'de elevation of the casing represented partially in section and showing in dotted outline the American type filter represented in Fig. 1.'

Fig. 3 is an assembly view of a complete installation showing one method of connecting the filter with its .auxiliary equipment yfor operation.

Fig. 4 is a fragmentary View of one end of the casing showing the manhole which provides convenient means for a man and supplies to enter the casing.

Fig. 5 is a, sectional view of the Valve located at the end of the filter and shows the respective position of ports to which communciation is established through the flexible hose connections vshown in Figures 1 and 2.' i

Fig. 6 shows an end view of the casing provided with a lock through which a man may enter or leave the shell when desired y without reducing the pressure in the casing.-

" is used in Figures 1, 2 and 3, but in this instance a drum type of filter is shown in side elevatlon 1n place of the -American or disc means of the bolts 3. Located near the bottom of the shelland on the inside thereof are bracket supports 5 upon which the rails 6 are mounted to form a track parallel to the axis of the cylindrical casing. A runway 7 mounted upon a bracket 8 provides a convenient place for a workman to stand while making repairs or adjustments. Rigidly mounted upon the side of the bracket 5 is a hopper 9 which is designed to receive the residual matter or cake which is discharged from the filter during operation. The lower portion of the hopper 9 is rounded to conform to .the spiral screw conveyor 10, the purpose of which isto remove accumulated residues from the casing. At the bottom of the casing is a discharge pipe 12 which is provided with valve 13 actuated by the lever 14 and the float15. This float valve arrangementl automatically provides an exit for material overfiowing from the filter as will be described in more detail later. i

Mounted upon the rails 6 by means of the flanged wheels 16 is a type of filter well known in the art as, the American continuous vacuum filter, and embodied for example in the United States Patent #1,259,139. As no invention pertaining to the details of the filter itself are herein claimed and as the machine is well known in the art minute description is not considered necessary. The main parts of this filter consists of the supports 17 upon which is mounted the tank or pan 18` which is supplied with an overfiow spout 19. A plurality of discs are formed by the sectors 20 and these are held in. position' on a rotating center shaft by means of radial rods which terminate in the nuts 21 which bear against the sector clips 22. Each of these sectors is covered with a suitable filtercloth stretched over a drainage-member in such manner that the filtrate may pass ino lla'i Jthrough the filter cloth and on through suitablev ports in the center shaft and finally out through the hose 23. The center shaft with its discs formed by the filter-cloth-covered sectors are caused to rotate by means of the motor 24, the speed of whlch is reduced through gears contained in the housings 25 and 26 and finally through a worm in the housin 27 and wormgear in the housing 28. The le hand side of the pari 18 as shown in Fig. 1 is provided with a series of notches between the filter discs. These notches exlau .dotted line 29 and thus provide spaces for the residual cake which is removed from the discs by the Scrapers 30 tofall into the hopper 9. These spaces are indicated by the numeral 29--A in Fig. 2. An apron plate 31 isprovided to guide the falling residues mto the hopperl 9. The material to be fil# tered enters the pan 18 through the pipe- 32. The pipe 33 is the inlet through which compressed airis admitted to create the desired pressure within the casing. The casing 1 rests upon supports 34 which are preferably arrangedin line with the brackets 5 so that the weight of the filter will have no tendency to distort the shell or casing.

In Fig. 2 the side elevation of the American filter is shown and this view particularly shows the method of connectin the various conduits which have to do wit the operation of the filter through the end of the casing. It will be noted that the screw conveyor is operated through the shaft 35 by means of sprocket 36 and that the screw conveyor 10, a greater portion of which lies in the open hopper 9, is slightl tapered at the discharge end and is enclose near the end in the hous- 1ng '37. A valve 38 is provided at the discharge end and this valve in conjunction with means of regulating the speed of the sprocket 36 provides for a variation in rate for discharge of residues as may be required to suit different materials. The spiral screw type cf discharge apparatus is illustrated merely as representative of one type of apparatus which may be used for this purpose,

and other devices such as a piston or intermittent opening gate may be employed without departing 'rom the spirit of my invention. The manhole 39, Windows 40, electric lights 41,? and their attendant wiring`42 are shown in this view. The insulators 43 provide means for supplying power to the motor 24 through the wires 44. A lug 45 on the cover 4 is provided to facilitate handling the cover. The liquid to be filtered enters the casing through pipe 46 which by means of the union 47 is attached to pipe 32. Filtrate is-l sues from the casing through pipe 48 which by means of the union 49 and hose 23 communicates with the portion ofthe valve which is indicated by the numeral 51 in Fig. 5. The pipe y52 through the union 53 and hose 54'communicates with the port of the valve shown in Fig. 5 which is indicated by numeral 55. This pipe is used for exhausting the moisture from-the cake duringthe drying period an'd to prevent excessive loss of air through the cake, the valve 56 is provided. By throttling--this valve the amount' of air whlchescapes with the moisture may be regulated. Pipe 57 is for the admission of compressed air to the interior of the filter sectors to which it communicates through the space indicated by the numeral 58 in Fig. 5 by means of the union 59, and the hose 60.

Referring to Fig. 3 the air compressor 61 is assumed to be provided with an automatic unloading valve 'so that it maintains a pressure, say of 60 pounds per square inch in ing valve which is diagrammatically represented by 64. The construction of this valve is such thatit maintains a pressure, let us the tank 62. The pipe 63 enters the regulatsay, of 50 pounds per square inch in the tank A 65. The valves 66, 67 and 68 are used only for convenience in case `repairs are necessary. Theliquid to be filtered is stored 'in the tank 69 and is pumped into the casing by means. of the pump 70 which communicates with p1pe 46. The pipe 12 which communicates with the ioat valve inside of the filter casing is here shown in position to return back to the tank 69 any liquid that might be discharged through the float valve 1 3. In some cases it may be desirable to make the shell somewhat smaller in proportion than that shown in Fig. 1 for purposes of economizing in first cost of the tank, and in this instance ample working room would not be provided within the shell and it would be desirable to remove the filter from the shell if extensive repairs were needed. To facilitate removal of the.

filter in such cases I provide rails 71 supported upon a suitable structure 7 2 and these rails are made to align with the rails 6 within the casing. This arrangement makes it possible when the head is removed to insert two short rail sections to connect the rails 7l with the rails 6, and thev il-ter'inits entirety may then be rolled out of the casing for any purpose whatever.

Referring to Fig. 5 it should be understood that each row of sectors 20 communicates with a conduit extending throughout the length of the shaft and communicating with a port in the valve at the' end of the lter. For example all of the sectors along the line indicated by the letter A in Fi 5 communicate with the ort A in t e valve. Those indicated by t e letter B communicate withI the port B of the valve, and those indicated by the letter C with the port C of the valve and so on. Theinner member or plug of the valve 74 is the member to which the hoses 23, 54 and 60 are connectedand this member remains stationary during the operation of the iilter. The outer portion of the valve 75 rotates with the shaft. It will therefore be seen that as the shaft and its filtering discs rotate in counterclockwise direction the various rows of sectors progressively come into communication with the ports in the plug of the valve indicated by the numerals 51, 55 and 58.

Fig. 6 v shows the details of a lock at the end of the casing. This consists of the small casing 76 which is connected to the end of the casing 1. A man may enter this casing through the manhole 77 after which it is closed and the pressure in casing 76 is gradually brought up to a pressure equal to that within the casing 1. When this time arrives the manhole 39SL is opened and the man enters the casing, and after performing his mission returns through manhole 39, which he then covers and the pressure is gradually relieved from casing 76 through the valve 7 8 until it has reached atmospheric pressure. -He may then exit through manhole 77.

l F ig). 7 shows a horizontally divided casing The drum type of filter 88 shown in Fig. 8 is operated upon the same principles as those employed in operating the American type filter shown in theother figures, and the procedure will be obvious to those skilled in the art after, having familiarized themselves with the technique of operating the American type filter.

Referring to Fig. 9 there is attached to the end of the casing 1 a large pipe connection 80 4 to which'is attached a valve 81 and a tank or Meth-oci of operation It should be understood that the normal method of operating the American continuous suction filter herein described is substantially as follows:

(ill

Suction is applied to the hose 23 while the filter discs are rotated at a rate, let us say, of one revolution in three or four minutes. The lower portion of the discs being submerged in the liquid to' be filtered the filtrate is drawn through the port 51 (Vig. 5) causing a deposit of cake to form upon the filter surfaces. In this instance suction is also applied to the hose 54 and communicates with the interior ofthe filter sectors through the port 55. This suction through hose 54 causes a partial drying of the deposited cake as it progresses in its revolution until the sectors come in communication with the port -58 which is supplied witlil` compressed air through the hose 60. Thej reverse current of compressed air thus produced causes the filter cloth to swell out and discharge the cake Pwhich is scraped off of the cloth byA means of the scrapers 30 and the cake then?.V

drops down through the spaces 29a off/.the an 18 and are carried away from thefilter y any convenient means. Operating under these conditions filtration is induced only by the differential between atmospheric pressure and the rarifed vcondition produced within the sectors by the partial vacuum produced bythe suction pump. Under normal condit-ions the suction produced yields an effective filtering pressure equal to only ten or twelve pounds per square inch. On account of this comparatively low filtering pressure it is necessary to revolve the discs very slowly and even then such a filter is applicable to only free filtering material.

' In operating the same filter under the method herein described and claimed, I am not dependent upon atmospheric pressure but create artificially high pressure in the atmosphere surrounding the filter so that if a pressure of 50 pounds per square inch is maintained within the casing which surrounds the filter the rate of rotation may be greatly increased and the production of the filter multiplied accordingly.

The operation of the apparatus by my invention is as follows:

Tank 62 being maintained at a pressure, say, of' 60 pounds per square inch or more, and valves 66, 67 and 68 being opened, the special regulating valve 64 functions in such manner as to maintain a uniform pressure of, say7 50 pounds per square inch within the casing 1 and a pressure of, say, 55 pounds per square inch in the tank 65. The pump 70 is started in operation, pumping the liquid to be filtered from tank 69 into the filter pan 18 until the latter begins to overflow through the spout 19. At this point the -motor 24 is started in operation causing the filter discs to rotate in counter-'clockwise direction at the rate, say, of one revolution per minute. Since the pipe 48 which carries away the filtrate is open to the atmosphere, discharging the filtered liquid into any convenient receptacle, there is a difference in pressure between the interior of the filter elements and the exterior of same equivalent to 50 pounds per square inch and this causes the filtrate to discharge at a rapid rate through pipe 48.

AAs the filter elements rotate they pass out ofy communication with the port 51 of the valve represented in Fig. 5 and advance with a load of deposited filter cake into communication with the port 55 of the same valve. At this stage the sectors are out of submergence but are surrounded by compressed air -at 50 pounds pressure per square inch, which forces -its way through the cake. carrying the excess moisture with it, and this mixture of moisturev and compressed air discharges through the pipe 52, the valve 56 being regulated so that an excessive amountof compressed air does not escape. During this phase of the cycle the cake is dewatered as far as it may be by'filtration methods. The sectors advance out of communication with the po.. 55 and into communication with port 58 which'is continuously supplied With compressed airfrom the tank through the pipe 57 at a pressure a few pounds per square inch higher than the pressure within I the casing. -This unbalancedpressure results in a reverse current of air passing through the filter cloth on the sectors, causing the filter cloth to bulge outwardly so that it is brought into bearing with the Scrapers' 30 I and the cake is thus discharged from the cloth and falls into the hopper 9. The air which is thus discharged through the lter cloth tends to' replenish the compressed air which is exhausted through .pipe 62 and valve 56.

It is assumed, of course, that while the machine is in operation the sprocket 36 is being caused to rotate the screw conveyor 10 and theresidual cake is thus discharged from vthe ilter casing Ythrough valve 38 which is regulated to give the proper rate of discharge. The housing 37 throu h which the screw 10 operates is naturally ept plugged' with residual cake which is compressed by the action of the screw and thus prevents the escape of compressed air through the valve pipe-12 and returns back to the tank ce..

The discharge of the pump is regulated either manually or automatically so as to maintain the proper liquid level in the pan 18 and under normal conditions would be so regulated as to maintain a slight overiow through the hopper 19 and the excess un'- flltered material which overflows is in turn discharged by the float valve 13 through the f desired, the motor 24 may bemounted outside of the casing, in whlch event the power for rotating the filter would be trans-V mitted through a suitable shaft passing through a stuiiing box which would preferably be located on the head of the casing adjacent vto the drive ears. Y*

` When operating y means of vthe apparatus shown 1n Fig. 9 the screw conveyor 10 d1s charges the residues through the pipe 80 and valve 81 into the tank 82 which normally Vwould be designed to hold several tons of residues. When it is desired to dischar these residues the valve 81 is closed and t e air in'this tank is exhausted through the valve 87 after which the door 84 is opened and the residues .discharged into a car or other suitable receptacle. The door 84 is then closed and locked and valve 81 opened and the operation continues. Obviousl two or more locks 'of this character could he attached to the shell if desired, so that. one

could be discharged while the other is filling..

The operation of washing the cake on the American'filter or on the drum type of filter by means of sprays playing uponthe cake deposited on the sectors 20 may obviously be employed in connection with my proces by simply mounting suitable spray nozzles n proper relation to the lter sectors, and

1 forcin water through them from the out-V side o the casing at a preure in excess of 50 pounds per square inch. As this step -appears to be obvious it has not been thought necessary tol complicate the drawings and specifications with this feature, although such a washing operation is clearly within the purview of this invention.

It is also within the scope of thisinven tion to employ a rotating type of filter having an intermittent motlon as described in my U. S. Patent No. 1,432,134 issued October 17, 1922, or modifications thereof, if desired.

Many modified forms of casing and of A auxiliary apparatus may be employed without departing from the spirit of my invention, and I do not wish to be limited to the specilic constructions herein shown and described.

While under ordinary conditions the gas which would be compressed within the cas-v ing would be ordinary air I reserv the right to employ any other gas that may be advantageously used in connection with any particular filtration process. For instance in certain processes it may be desirable to employ nitrogen orv carbon dioxide or other gas which would tend to prevent oxidation of the materials under" treatment in the filter. In other cases a special gas such for instance as sulphurous gas for the purpose of providing a bleaching effect or to promote some desiredchemical reaction may he employed.

Wherever the term suction filter is used in the following claims it is intended to mean any type of filter which is designed and normally intended to beY used with a suction' pump, or other means of creating a partial vacuum in the interior of the filter elements for the purpose of drawngltrate through .the filter cloth. Such filters. are sometimes called vacuum ilters and in some installations a wet vacuum pump is used, which' draws the filtrate directly through the pump, and in other cases a dry vacuum pump is used to exhaust a receiving tank into which the Iiltrate Hows. As any of these types may -be ing an enlarged separate sealed casing and causing it to operate by surrounding the entire filter with a gas under pressure.

3. A method of operating a'lter designed mi I lter having an independent mounting withand built to operate normally as a continuous rotary suction filter having an independent portable mounting Whichconsists in enclosing said filter within a sealed separate casing and surrounding the entire filter mechanism with gas under pressure.

4. A filter room comprising a shell, a continuous vacuumrotary filter, a normally sealed closure of such size as to admit the installation of said filter, said filter having a tank surrounding the lower portion of the filter elements for containing the liquid to be filtered, and said tank being independent of the filter casing and means to place said filter in or out of said shell as desired.

5. A filtering apparatus comprising an airtight casing adapted `to receive a complete portable filter unit and of such proportions as to allow working space for a man between the walls of the casing and the filter parts, a normally sealed door through which a man may enter the casing, said filter unit being of the type normally operated by vacuum and operable under super-atmospheric pressure in said casing.

6. An air-tight filter casing, a portable rotary vacuum filter within the casing, means for continuously operating the filter at a super-atmospheric pressure by means of a compressed gas surrounding the filter, means to bodily remove said filter from said casing and means to operate under vacuum conditions. .J 7. A filter apparatus comprising an outer air-tight casing surrounding a rotary filter unit having a portable mounting, said casing being independent of' the operable unit, a tank within the casing for containing the liquid to be filtered, a space between said tank and said casing, means for maintaining a uniform gas pressure within the` casing and means for removingsolids from said casing Y without affecting the pressure.

8. A filter casinghaving a rotary filter unit of the class described, portably mounted within the casing, a tank for holding the liquid to be filtered within the casing and a valve within the casing for progressively opening and closing communication between the various filter elements, and a conduit passing thru a wall of the casing.

9. An air-tight room adapted to receive a filter installation, said installation including an integrally complete operable suction type filter, means for maintaining gas under pressure within the room, a sealed closure whereby a man may enter or leave the filter room,

and space within said room to permit a man to work between the Walls of the room and the filter installation.

10. An air-tight room adapted to receive a suction filter installation having a portable mounting, said room including a large cylin- Lirical-chamber and removable head thereon,

means for maintaining gas under pressure within the room, a sealed closure whereby a plete suction type filter portably and independently mounted therein, and having the operating parts ofsaid filter built independently and separately of said casing.

12. A filtering apparatus comprising a separate air-tight casing and a sealed door for said casing and a complete filter unit of the so called suction type having an independent portable mounting, mounted within said casing, and means to operate said filter either in or out of the casing.

13. A filter apparatus comprising a separate outer shell having a self-contained filter unit of the so-called suction type. removably mounted therein and having a tank in which a plurality of filter elements are caused to revolve, said tank being constructed independently of the outer casing.

14. A filtering apparatus comprising an outer casing having a substantially complete filter unit of the continuous rotating type slidably mounted within the casing, a door upon one end of the casing to permit the filter unit to be slidably removed from said-casing in a horizontal direction, means to seal said door against filter pressures and means to operate said filter under pressure or vacuum.

l5. Means for converting a suction or vacuum filter to a pressure filter having an independent portable mounting which comprises a separate casing, means in said casing to receive a vacuum filter, mea-ns to removably position the vacuum filter in said casing, means to seal said casing and means to kintroduce a pressure medium therein to perlous vacuum filters to pressure filters which comprises a shell, suitable brackets therein upon which a complete filter of the vacuum type may be removably mounted, means within the shell and independent of the filter for' receiving the residues from the filter, means for discharging them from the shell, and means to seal said room.

18. An article ofmanufacture, a filter room for converting vacuum filters to pressureA filters comprising an enlarged casing, a ref progressively opening and closing communisaid filter extending outside said pressure.

casing to permit operation vof the filter at cation between the various filter elements and a conduit passing-thru the Wall of the casing.

20. In a filtering apparatus of the type described including a continuous filter having a sludge compartment, a filtering portion movable thru the sludge compartment and a'.

pressure casing independent of said sludge compartment adapted to surround said filter and sludge compartment and to permit operation of said filter at a superatmospheric pressure.

21. In a filtering apparatus of the type described including a continuous filter having a sludge compartment, filter elements movable thru the sludge compartment and a pressure casing independent of said-sludge compartment and flexible connections between superatmosfpheric pressure means.

22. In a ltering apparatus of the typedescribed including a continuous filter having a sludge compartment, filter elements movable thru the sludge compartment, a pressure casing independent of said sludge compartment adapted 'to surround.I filter and Isludge compartment, saidy continuous filterbeing provided-with rollers andsaid pressure casing being rovided with rails cooperating with said ro ers-@hereby said continuous filter may be placed or out of said pressure casing. y

23. An airtight filter casing having a complete suction typeiilter mounted-therein, the operating parts of said filter being built independently of saidcasing and including afioat valve controlling the height of liquid in the outer casing and independent of the level of liquid in the lter proper.

24. An airtight filter casing having a complete suction type filter mounted therein, said filter including a driving motor entirely enclosed and within the separate airtight filter casing. v

25. In a filtering ap aratus of the class described a continuous fil tank, filter elements operating in said sludge tank',means for removing the filter cake from said elements, a receiving chamber for said cage externai of said filter, a separate airtight casing independent of said sludge tank and'entirely surrounding said filter and said ter having a sludge' discharge chamber, said chamber being ofl such capacity that it will permit substantial accumulation of cake between. the discharge elements of the filter and said casing.

26. An airtight filter casing having a complete suction type filter mounted therein, said filter having a sludge tank, an overfiow from said sludge tank, a float valve controlling the liquid level in said filter casing,` said float valve. and said overflow maintaining a sub- Vstantially constant level of sludge in the sludge tank.

27.; In a filtering apparatus of the-type described including a continuous filter havinga sludge compartment, filtering parts movable thru the sludge compartment, apressure casing independent of said sludge-com--- partment adapted to surround said filter and to permit operation 'of the lter under superatmospheric pressure and a pressure lock in communication with said pressure casing adapted to receive the discharge filter cake without loss of pressure.

28. An airtight filter casing having a comi plete suction type filter mounted therein,

'means to discharge filter cake from said filter into said separate airtight casing and a pressure chamber in communication with said separate casing adapted to receive said discharge cake under pressureand Without loss of pressure in -said separate casing.

29. An airtight filter casing having a complete suction type filter mounted therein, means to discharge -filter cake from said filter into said separate airtightcasing and a pressure chamber in communication with said separate casing adapted to receive said discharge cake under pressure and without loss 'of pressure in said separate casing, said pressure lock being provided witha conical ottom and a pressure discharge pipe to facilitate discharge of large quantities of residue. p

30. In a filtering apparatus of the class described, the combination of a suction filter having a sludge tank, filter elements adapted to pass thru said sludge tank, -a motor to drive said filter elements, a discharge mechanism to remove the filter cage from said filter elements, and a separate airtight pressure casing completely surrounding said suction filter and independent of said sludge tank, flexible connections between the Wall of said pressure casing and said suction filter, a valve mechanism on said filter, roller means to permit the movement of said suction'filter into and out 'of said pressure casing, a sludge discharge receiving chamber in said pressure casing adapted-to receive the filter cake from yserved externally, said pressure casing being of such size that a man maybe accommodated Within said casing during the operation of said filter and means entirely within said casing to maintain a substantially constant level yof sludge in the sludge'tank.

31. The method of maintaining a constant sludge level in the sludge compartment of Va continuous pressure filter which comprises providing an overflow outlet at the desired evel and pumping sludge through the sludge compartment at a sufcient rate to maintain a slight overow at all times.

32. Ina continuous pressure filter installation, a sludge compartment, filter elements movable through the sludge compartment, means to maintain superatmospheric pressure on said filter elements and on the sludge in said compartment and means to maintaina constant level of sludge in said compartment, comprising means to force sludge into the compartment at a pressure greater than the filtration pressure and an overflow from said compartment through which the excess sludge Hows out at the level of said overflow. n

In testimony whereof I have aixed my signature to this specification.

` ERNEST J. SWEETLAND. 

